1. Field
The present invention is directed to an engine having a combustion piston linked with a fluid power assembly to pressurize a fluid, a portion of the pressurized fluid being returned to urge the combustion piston in the direction of its return stroke.
2. State of the Art
Internal combustion engines typically have one or more pistons linked with a crankshaft. After ignition of the fuel, energy released from the ignited fuel is delivered to the crankshaft, which rotates in response to the reciprocating motion of the piston. This energy is typically ultimately delivered to a machine that the engine is adapted to power. A common use of internal combustion engines is, of course, their use in automobiles.
Crankshaft-style internal combustion engines in automobiles inherently allow for energy loss at various junctures. For example, energy is lost through friction in the transfer of the reciprocating motion of the piston to rotational motion of the crankshaft. Further energy is lost in transferring the rotational motion of the crankshaft to rotation, for example, of parts within a transmission, differential, and ultimately the wheels of the automobile. The engine is subject to vibration and wear at various locations due to internal forces exerted on various mechanical parts.
One engine design that eliminates a crankshaft is known as the "free piston" engine. Free piston engines typically have two opposed pistons connected by an axial shaft. They are typically two-stroke engines, and are typically used as air compressors.
A problem with free piston engines is that as the work load that the engine is operating against increases, the engine may power down more easily than a crankshaft-style engine. The free piston engine does not have the rotational momentum of a crankshaft to aid in returning the pistons in the direction of their return strokes.
Fluid power systems are recognized as being highly efficient. Once fluid pressure is generated within a system, that pressure is transmitted essentially instantaneously throughout the fluid in the system and is immediately available for work at selected points in the system. Hydraulic systems are particularly useful because of the essential noncompressibility of liquids. When crankshaft-style engines are used to develop fluid power, the reciprocating motion of the combustion piston is transferred to rotational motion of the crankshaft, which is then transferred in some form to a pump to pressurize the selected fluid.
Free pistons have been recognized for their utility in air compressors because the linearly reciprocating motion of the combustion piston may be transferred directly to a linearly reciprocating pumping piston of a compressor piston. However, once a substantial load is placed on the engine in a fluid power system (pneumatic or hydraulic), the power-down problems previously discussed may occur.
There remains a need for an engine adapted to be useful in a fluid power setting that avoids the power-down problems of currently known free piston engines while avoiding the energy losses inherent in a crankshaft-style engine.